The present invention relates to a suspension polymerization process suitable for preparing coordination catalyzed polymers of vinyl aromatic monomers. More particularly the present invention relates to a process suitable for the preparation of vinyl aromatic polymers having stereoregular structure of high syndiotacticity.
In U.S. Pat. No. 4,680,353 there is disclosed a process for the preparation of polymers of vinyl aromatic monomers having stereo regular structure of high syndiotacticity by the use of coordination catalysts, particularly certain transition metal catalysts. The process disclosed in the foregoing U.S. patent is a solution polymerization wherein the vinyl aromatic monomer is initially dissolved in a suitable inert liquid solvent and the so dissolved monomer thereafter contacted under polymerization conditions with the appropriate coordination catalyst. The resulting polymer possesses a highly crystalline nature and consequently becomes insoluble in the reaction mixture. However, at the same time the polymeric product is highly swollen by the solvent and readily forms an intractable gel-like structure preventing the necessary homogenization of the reaction mixture. As a result the reactor is rather quickly fouled with this polymer gel. Because of this reason catalyst efficiencies in the solution polymerization process disclosed in the foregoing U.S. patent have been found to be relatively low, while at the same time heat removal and product recovery are particularly difficult. It is therefor understandable that scaling the reaction disclosed in the foregoing U.S. patent to commercial sized reactors has proven problematic and impractical.
It is previously known in the art to prepare atactic polystyrene by means of a suspension process. However, the suspension polymerization of atactic polystyrene has previously employed a free radical catalyst and the suspending medium has been principally water or similar nonsolvent liquid. Disadvantageously, however, typical coordination catalysts are highly reactive with water or other polar, protic solvents. Accordingly it is not possible to prepare vinyl aromatic polymers utilizing coordination catalysts according to previously known suspension processes.
It would be desirable if there were provided a suitable suspension process for the preparation of coordination catalyzed vinyl aromatic polymers. More particularly it would be desirable to provide a suspension process wherein the coordination catalyzed polymerization of vinyl aromatic monomers may be conducted in high efficiency and convenience and in volumes sufficient for commercial purposes.